When practising Maths, the Skills section gives around five questions. The five questions tend to be so that some of them are Calculator Ok and others are No Calculator questions. Unfortunately, with just the small icon at the top, I often miss if its a Calculator or No Calculator section, and end up using the calculator for non-cal sections (and vise versa).

I would like to suggest either making that icon bigger and more obvious for each question or making it so that each mini 5-question section tells you beforehand that the five questions you are about to do is either Calculator Ok or No Calculator.